Kuala Lumpur: Kim Jong-Nam was dead within 20 minutes of being attacked and would have suffered a "very painful death" as his major organs shut down, Malaysia's health minister said on Sunday.

The estranged half-brother of the North Korean leader was killed with lethal nerve agent VX, police have revealed, after he was ambushed at Kuala Lumpur airport on February 13.

A reporter holds up a local newspaper during his report in front of the morgue at Kuala Lumpur General Hospital where Kim Jong Nam's body is held for autopsy in Malaysia . Reuters

Two women can be seen shoving something into Kim's face in leaked CCTV footage of the brazen assassination before he seeks help.

"He died in the ambulance. He fainted in the clinic," Health Minister S Subramaniam told reporters.

"From the time of the onset (of the attack) he died within 15 to 20 minutes."

Autopsy results suggested the 45-year-old died from "very serious paralysis" due to a lethal nerve agent, Subramaniam said earlier Sunday.

Police are holding two women suspected of staging the attack as well as a North Korean man.

They want to speak to seven other North Koreans including a senior embassy official, but four of the suspects fled Malaysia on the day of the murder.

VX is so deadly it is listed by the UN as a weapon of mass destruction and overnight the scene of the killing in the budget terminal of Kuala Lumpur International Airport was swept by civil defence personnel in hazmat suits before being declared safe.

"VX only requires 10mg to be absorbed into the system to be lethal," Subramaniam said.

"The absorption level was so rapid that within a few minutes the guy had symptoms."

Nerve agents prevent the proper operation of an enzyme that acts as the body's "off switch" for glands and muscles.

Without that switch, glands and muscles are constantly being stimulated, eventually tire and become unable to sustain breathing.

"The muscle goes into a state of permanent contraction," Subramaniam said, adding the dose was "so high" in this case the heart and lungs would have been rapidly affected.

Police had cordoned off parts of the airport after authorities pledged to check all locations the female suspects were known to have visited.

But the delay puzzled some travellers.

Student Hariz Syafiq, 21, who was due to take a domestic flight later, told AFP: "Yes, I'm worried a bit. Why didn't they quarantine the airport?

"It's a bit strange."

Both women suspected of carrying out the attack insisted they thought they were taking part in a prank video, although Malaysian police have said they knew what they were doing.